Heretofore, in an electronically commutated DC motor, often called a "Brushless DC motor" or a BDCM, the position of the output shaft was determined from a feedback transducer for limited motion position control servos. Typical of such feedback transducers are linear variable differential transducers and rotary variable differential transducers both of which respond to mechanical position to generate a position feedback voltage to control the output shaft position.
One application where DC motors and feedback transducers have found extensive use is in direct drive hydraulic servo valves. Such servo valves are used for position control of a power actuator. In many such applications the environment surrounding the servo valve and in turn the motor itself varies erractically and over a wide range of conditions, such as from very low temperatures to very high temperatures. In such an environment many factors enter into the accuracy of the position control for the DC motor.
The present invention may be used for controlling the operation of small, brushless, variable output or variable speed motors for aircraft control applications. However, it will be apparent that the invention may be equally applied to industrial power motors.
One application of the control system of the present invention is the positioning of a torque motor driven spool valve. Typically, such a spool valve includes a movable member disposed within a bore having an inlet and outlet port to provide communication between a supply passage and a load passage in a controlled fashion in response to the application to a torque motor of a motor position signal. This torque motor is operatively interconnected with a valve member that is positioned in accordance with the motor position signal. It is the load passage of such spool valves that is connected to an actuator as described. Typical of U.S. Patents issued on inventions relating to spool valves is U.S. Pat. No. 3,040,768, entitled "Oscillating Valve". The control system of the present invention finds utility in connection with such servo valves.